Distinguishing active generators from exhausted ones

[Terry Reedy]

Steven D'Aprano wrote:
> On Sun, 26 Jul 2009 20:10:00 -0400, Terry Reedy wrote:
> 
>> Michal Kwiatkowski wrote:
>>
>>> The thing is I don't need the next item. I need to know if the
>>> generator has stopped without invoking it.
>> Write a one-ahead iterator class, which I have posted before, that sets
>> .exhausted to True when next fails.
> 
> 
> And hope that the generator doesn't have side-effects...

If run to exhastion, the same number of side-effects happen.
The only difference is that they each happen once step happpen sooner. 
For reading a file that is irrelevant. Much else, and the iterator is 
not just an iterator.

tjr